Effects of very low piston speed regimes on near-isothermal behaviour of piston expanders for micro-CAES systems
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Research Project
ID: 501.00-210000-10000
UB-696000-00001-Z01
2024/55/I/ST8/00539
BPI/PST/2024/1/00046
UB-696000-00001-Z01
2024/55/I/ST8/00539
BPI/PST/2024/1/00046
Institution: Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)
Narodowe Centrum Nauki (NCN)
Narodowa Agencja Wymiany Akademickiej (NAWA)
Narodowe Centrum Nauki (NCN)
Narodowa Agencja Wymiany Akademickiej (NAWA)
Program: Inicjatywa Doskonałości - Uczelnia Badawcza (IDUB AGH)
OPUS 28+LAP/Weave
Partnerstwa strategiczne
OPUS 28+LAP/Weave
Partnerstwa strategiczne
Description
The development of highly efficient, long-term electricity storage technologies is of major interest to scientists and engineers [1]. One promising solution is compressed air energy storage (CAES), which enables long-duration storage with flexible power and capacity. However, its wider adoption—particularly in small and micro-scale systems below 1 MW—is limited by low efficiency and high investment costs. Thermodynamic processes in micro-CAES systems can be classified as near-isothermal, near-adiabatic, or polytropic, depending on heat transfer conditions and operating speed. Typical rotational speeds range from several hundred rpm for piston expanders to tens of thousands of rpm for turbomachinery [2]. Gao et al. [3] showed that a solid-piston system operating at reduced speeds (≈200 rpm) can achieve internal isothermal efficiencies up to 95%. Dib et al. [4] compared solid and liquid pistons with water injection, demonstrating that a liquid piston can reach a polytropic exponent close to 1.0 with a heat transfer coefficient of 10 W/m²·K, while a solid piston requires approximately 500 W/m²·K to achieve a similar effect. Their study, however, focused on engine-based machines operating at several thousand rpm. Despite extensive research on near-isothermal volumetric machines, the influence of very low rotational speeds (30–100 rpm), characterized by long thermal relaxation times, remains insufficiently understood. In particular, the combined effects of low-speed operation on heat transfer and the resulting polytropic exponent during air expansion are unclear. This study experimentally investigates a piston expander operating at very low rotational speeds relevant to micro-CAES applications. The effects of operating pressure (4–8 bar) and rotational speed (30–100 rpm) on the air expansion process and polytropic exponent are analysed. The results highlight the role of extended thermal relaxation time in near-isothermal expansion and increasing roundtrip efficiency of micro CAES over 70%.
7th International Conference on Energy and Environment: bringing together Engineering and Economics; Porto(Portugal); 18-19 June, 2026.
7th International Conference on Energy and Environment: bringing together Engineering and Economics; Porto(Portugal); 18-19 June, 2026.